In general, a machine tool is configured by a combination of various constituent elements such a bed frame, a column frame, a cross frame, a table unit, a turret unit, a transfer table unit, a spindle, a sub-spindle, a tailstock, and the like.
Meanwhile, a structure of the machine tool may be separated into a fixed structure and a movable structure, the movable structure is installed on the fixed structure, and the movable structure moves while performing relative motion with respect to the fixed structure.
The fixed structure may be the bed frame of the machine tool, and the movable structure may be the transfer table unit or the column frame of the machine tool.
In addition, because another movable structure may be moved by being installed on the movable structure, a particular movable structure may be understood as a fixed structure, and for example, the turret unit may be installed on the transfer table unit, and in this case, the transfer table unit may be understood as the fixed structure, and the turret unit may be understood as the movable structure.
As described above, heat due to friction is generated at the part where the fixed structure and the movable structure come in close contact with each other when the fixed structure and the movable structure move together with each other, and the heat causes thermal deformation of the fixed structure or the movable structure.
In addition, because a relative position of the movable structure with respect to the fixed structure is varied when processing of a work piece proceeds, a position at which heat is generated may be varied.
Particularly, temperature differences of the structure occur between parts to which heat is applied and parts to which heat is not applied, and because amounts of displacement of expanded parts are different from each other due to the temperature differences, distortion of the structure occur.
This thermal deformation causes problems in that processing precision of the work piece deteriorates, and further, processing quality of the work piece is lowered.
As technologies contrived in order to cope with the problems due to thermal displacement, the following Patent Literatures 1, 2, and 3 have been disclosed.
Patent Literature 1 relates to a cooling apparatus for a machine tool structure capable of reducing an error due to heat generated in a transfer system of the machine tool, which suppress heat, which is generated inevitably, by forming a cooling flow path in a ball screw shaft of the transfer system for transferring tools as well as a cooling flow path formed to prevent thermal deformation of a ball screw shaft of a spindle system.
Meanwhile, in Patent Literature 1, the respective cooling flow paths are connected to an inlet and an outlet of a provided cooler so as to be able to be circulated, and a temperature controller is included in the cooler so as to compare a temperature of discharged oil with a temperature of the atmosphere, and cool oil flowing into the inlet.
However, in the technology disclosed in Patent Literature 1, because a large number of peripheral devices such as an oil tank, a condenser, an evaporator, an expansion valve, various pipes, and the like are required in order to cool and circulate oil, a configuration of the cooling apparatus is complicated, and a number of precautions are required to perform maintenance management thereof.
Patent Literature 2 relates to a cooling apparatus for a machine tool that cools heat generated at a spindle head by forming an oil space between an outer wall and an inner wall of the spindle head, and supplying and circulating cooling oil from an oil tank to an oil space formed in the spindle head through a cooling medium line.
However, in the technology disclosed in Patent Literature 2, there are problems in that because a large number of peripheral devices are required similarly to Patent Literature 1 in order to circulate cooling oil, a number of precautions are required to perform maintenance management thereof, and because a cooling operation is limited to the spindle head, heat generated at other structures such as a bed frame of the machine tool may not be cooled.
In Patent Literature 3, a temperature sensor is provided at a part where heat generation is estimated, an amount of thermal displacement is detected based on information obtained from the temperature sensor, and an amount of relative movement with respect to the respective shafts is corrected by converting the displacement amount.
However, in the technology disclosed in Patent Literature 3, the amounts of movements of the respective shafts are corrected with numbers by calculating information provided by a plurality of temperature sensors using a S/W, but it is difficult to accurately estimate a direction in which a structure is distorted or deformed because environment (temperature, humidity, or the like) where the machine tool is installed and operated is varied, and processing forms for work pieces are various, there may be a case in which a result value, which is theoretically obtained, and a correcting value, which needs to be actually applied, are different from each other, and in this case, there is a problem in that it is difficult to perform precise processing.